This invention relates to storing, retrieving, transmitting, and receiving continuous-tone images.
In an image of the continuous-tone type, each point in the image can take on any value within a range of values, with value changes between nearby points typically being gradual rather than abrupt. In a gray-scale continuous tone image, each point takes on a gray tone in a range from white to black. In color images, each point may be construed as a composite of continuous-tone values each lying in a corresponding range associated with color features such as luminance and chrominance, or primary color values.
For purposes of digital storage and transmission, a continuous tone image may be divided into a matrix of a large, but finite number p of discrete "pixels". The value of each pixel may then be sampled and digitized as an n-bit number representing its position in the range of possible continuous tone values. The amount of information which must be processed and stored when the product of n and p is large makes it useful, and in some cases mandatory, to apply data compression and reconstruction schemes to the pixel values to reduce the amount of storage or transmission capacity required.
A wide variety of data compression schemes have been proposed and implemented.